Spot welder



Oct. 12, 1965 M. N. FISCHER SPOT WELDER Filed June 28, 1962 R o m w m Nw NOE 5 F N W T. R A M TUE Q mm :63 282 AR 5 800586 u M m @2533 n 185m 9@m u m P 4 mEQflE (64m 5301 vm m 053 $549 19: 2o; 9 u c o m mw2m8mz E A3 $5 9 MW i L KO-rm aw. uOmDw United States Patent 3,211,885 SPOT WELDERMartin N. Fischer, 2605 Gaither St., Hillcrest Heights, Md. Filed June28, 1962, Ser. No. 206,026 14 Claims. (Cl. 219-413) The presentinvention relates to welding apparatus and more particularly to anelectric welder capable of Welding a wide variety of materials having agreat diversity of sizes. This application is a continuation-in-part ofmy copending patent application Serial No. 126,438 filed July 13, 1961,for Portable Spot welding Tool, now Patent No. 3,050,618, issued August21, 1962.

The aforesaid copending application describes an electronic weldingapparatus capable of welding various size Wires fabricated from variousmaterials; particularly, wire leads on electronic components or wiresemployed as the interconnections between various electronic components.The welding system described in the said copending patent application isa capacitive discharge welder wherein a capacitor is charged to apredetermined voltage and then discharged through the primary winding ofa transformer having the welding electrodes connected to its secondarywinding. The voltage to which the capacitor is charged may be varied andis normally selected in accordance with the size of the wire and/or thematerial to be welded.

The commercial applicability of a portable welding tool which is to beemployed to weld electronic components is the ease with which the toolmay be employed. Various types of wire and the wire leads of electroniccomponents are employed in electronic systems as are various sizes ofwire. If it is necessary to employ a different voltage setting for eachwire size for each specific material from which the wire is fabricated,then the operator must carry a calibration chart for each set of factorsas set forth. Such a procedure is troublesome and calculated to producepoor or destructive welds. The desirable mode of operation is to permitthe operator to employ a voltage setting determined by only a singlevariable parameter.

In accordance with the present invention, there is provided anelectrical welding system employing a capacitor discharge circuit inwhich the voltage to which the capacitor is charged is a function of thesize or gauge of the material or wire to be welded. This permits anyexperienced technician to employ the apparatus with the greatest of casesince any trained technician can readily gauge wire size by eye and thenmake the appropriate setting.

The object of the present invention as set forth above is achieved byemploying a specific transformer in the specific circuit disclosed inthe aforesaid copending patent application. More particularly, thewelding transformer is designed to deliver a substantially constantcurrent over a relatively wide range of load impedance. The constantcurrent effect is obtained by winding a transformer with the primary andsecondary windings in substantially diametrically opposed positions on acylindrical core or on opposed legs of a square or rectangular core asthe case may be. The amount of core material is chosen such that, if thewelding load becomes too great, the core saturates and the degree ofcoupling between the primary and the secondary windings decreases tothat provided by leakage flux. In practice, the material employed has acurved premeability curve so that the degree of saturation of the coreand therefore the degree of coupling between the windings is a functionof the load current. In consequence, as the load current tends toincrease, the saturation of the core increases, the degree 3,211,885Patented Oct. 12, 1965 of coupling between the primary and the secondarywindings decreases and the current tends to stabilize. As an example, ifNo. 20 copper wires are to be welded, the constant current transformerprovides roughly the same current through the secondary winding as whenNo. 20 Nichrome wires are to be welded. As is well known the Nichromewire has a far higher resistance than copper and yet by employing thespecified transformer, the welding current generated in the secondarycircuit is maintained relatively constant. I

The welding transformer does not deliver completely constant current inthat there are variations in the secondary current when the variationsof loads become too great. Therefore, it is necessary to vary thevoltage" applied to the welding capacitor in accordance with wire sizesince it has been found that it is not possible with a practical weldingtransformer to accept all wire sizes of all different types of material.However, so long as adjustment is made in accordance with wire size, thetransformer is capable of maintaining a relativelylconstant currentregardless of the type of wire employed.

It is therefore an object of the present invention to provide anelectrical welding system employing a transformer that deliverssubstantially constant currents in conjunction with a capacitordischarge welding system.

It is another object of the present invention to employ a transformerthat delivers substantially constant current in an electric weldingsystem so that a single voltage setting may be employed to weldmaterials having widely different resistivities.

It is still another object of the present invention to provide acapacitordischarge Welder employing a transformer that deliverssubstantially constant current so that wires of the same size but ofdifferent materials may be welded by charging a capacitor to a specificvoltage and that different size wires regardless of material are weldedby adjusting the voltage to which the capacitor is charged in accordancewith wire size only.

The above and still further objects, features and advantages of thepresent invention will become apparent upon consideration of thefollowing detailed description of one specific embodiment thereof,especially when taken in conjunction with the accompanying drawings,wherein:

FIGURE 1 of the accompanying drawings is a schematic electrical diagramof a form of the welder of the present invention; and

FIGURE 2 is a three-dimensional perspective view of a weldingtransformer which may be employed in conjunction with the apparatus ofthe present invention.

Referring now specifically t-o FIGURE 1 of the accompanying drawings,high voltage from a power pack is coupled across a pair of leads 1 and 2in the welding circuit. The power pack may contain batteries or acombination of batteries and an A.C. rectifier supply if portability isdesired. It portability is not necessary, a rectifier supply may beemployed.

Connected in series between the leads 1 and 2 are a plurality ofresistors 3, 4, 6, 7 and 8. The resist-0r 3 serves as a surge resistorto preventexcessive surges of current from being supplied to the circuitand the resistors 4, 6, 7 and 8 serve as a voltage divider. A series ofswitch terminals 9, 11 and 13 are connected between the resistors 4 and6, 6 and 7, and 7 and 8, respectively, and are adapted to be engaged bya movablev contact 14. The resistors 4, 6, 7 and 8 provide predeterminedvoltages at the terminals 9, 11 and 13 so that the voltage to beemployed in a welding operation may be selected by the operator. Themovable contact 14 is connected to a lead 16, in turn connected to theupper end of a primary winding 17 of a welding transformer 18 having asecondary winding 19. Connected in series between the lead 16 and thelead 2 is a welding capacitor 21 and neon bulb 22 is connected via aswitch 23 to the lower end of the primary winding 17 of the transformer18. Welding electrodes 24 and 26 are connected in the two ends of thesecondary winding 19. It should be noted that the elements 3, 4, 6-9,11-14 may be completely eliminated if a variable, regulated power supplyis employed.

In operation, when the switch 23 is open, the capacitor 21 charges to avoltage as determined by the position of the movable contact 14 relativeto the contacts 9, 11 and 13. The charge time for the capacitor ischosen to be roughly three to four seconds although the time is notcritical. To effect a welding operation, the switch 23 is closed and thecapacitor 21 discharges through the primary winding 17 of thetransformer 18. The voltage generated in the secondary winding 19 of thewelding transformer causes a current to flow through a circuit includingthe secondary winding, the welding electrodes 24 and 26, and the weldingload. The operation of the circuit of FIGURE 1 has been describedbriefly above but is described in greater detail in the aforesaidcopending application.

The novelty of the apparatus of the present invention resides in theutilization with the circuit as illustrated in FIGURE 1 of a transformerfabricated as indicated in FIGURE 2. The transformer in one practicalembodiment thereof constitutes a hollow cylindrical laminated core 27having a primary winding 17 and a diametrically opposed secondarywinding 19. The winding 17 constitutes a large plurality of relativelyfine wires which for purposes of illustration may constitute a No. 20wire. The secondary winding 19 comprises a single turn of largecross-section wire which, for instance, may have a cross section ofone-quarter to one-half of an inch. The outside diameter of the core 27is approximately one and onehalf inches and its inside diameter isroughly three-quarters of an inch. The core is three to four inches longand the radial thickness of the core and of the winding 17 is such thatthe primary winding 17 and secondary winding 19 almost touch internallyof the core 27. The transformer step-down ratio is determined by therange of loads to be encountered and the specific uses to which theapparatus is to be "applied. Thus, ratios of between 100 to 1 and 2000to 1 may be employed. The value of the capacitor 21 depends upon the,step-down ratio of the transformer 18 and its inductance; for atransformer with a 600 to 1 step-down ratio and an inductance of 150millihenries, a SO-microfarad capacitor is employed. More particularly,the product of capacitance times inductance of the transformer may coverthe range from about 1 10 to about 100 10' The voltage delivered by thepower pack is again determined by the maximum load for which theapparatus is designed and may range from about 50 to 3000 volts.Adjustment of the voltage of a particular device is effected by means ofthe adjustable contact 14. A welder which has a maximum voltage of 400volts, a -microfarad capacitor and a 400 to 1 step-down ratiotransformer is capable of welding, as a maximum, a No. wire whereas a.machine providing 3000 volts, a 150-microfarad capacitor and a 2000 to 1step-down ratio is capable of welding, as a maximum, a No. 12 wire. H

The important feature. of the present invention is in the design of thewelding transformer which permits adju'stment of the movable contact 14in accordance with wire size only while disregarding the resistivity ofthe material being welded. This ability to adjust the welding voltage asa function of only wire size results from the fact that the design ofthe transformer illustrated in FIGURE 2 provides a substantiallyconstant current varying loads, In consequence, if the resistance of thewelding load is low, the core 27 saturates and reduces the couplingbetween the primary winding and secondary windings 17 and 29,respectively. On the other hand, if the current load is relativelysmall, the core does not saturate and maximum coupling is maintainedbetween the primary and secondary windings. When the core 27 saturates,the transformer appears to the primary circuit as an air coretransformer whereas when the secondary current is lower, the transformerappears to the primary circuit as an iron core transformer. Thus, thecurrent in the secondary winding is maintained constant and thevariation in coupling between the primary and secondary winding producesa variation in voltage such that the secondary current is maintained ata relatively fixed value. Thus, regardless of the resistance of the loadwithin the range of the apparatus, the current therethrough ismaintained constant and a single setting of the movable contact 14 canproduce proper welding of wires of the same size regardless of thematerial to be welded.

The Welding apparatus of the present invention has many of thecharacteristics of the welder disclosed in the aforesaid copendingapplication in that it is portable and employs a welding gun asillustrated in said application and weighing only two or three poundswith the entire device weighing approximately fifteen pounds.

While I have described and illustrated one specific embodiment of myinvention, it will be clear that variations of the details ofconstruction which are specifically illustrated and described may beresorted to without departing from the true spirit and scope of theinvention as defined in the appended claims.

What I claim is:

:1. A capacitive discharge system for welding wires of differentresistivities comprising a capacitor, means for charging said capacitorto a predetermined voltage, a welding transformer comprising a saturablecore, a primary winding and a secondary winding, means for at willdischarging said capacitor across said primary winding and meansconnecting a pair of welding electrodes across said secondary winding,said transformer having a saturation characteristic such thatsubstantially the same amount of current is supplied to wires ofsubstantially the same diameter, but of different resistivity, when thecapacitor is charged to said predetermined voltage, such characteristicexisting for welding currents into and below saturation of said core,said core being driven into saturation for wires having a lowresistivity.

2. A system for welding wires having the same diameter but differentresistivities comprising a'capacitor, a transformer having a saturablecore, a primary winding, a secondary winding, means for coupling thewires to be welded across the secondary winding, means for charging saidcapacitor to a predetermined voltage, means for discharging thecapacitor through the primary winding of said transformer, said lastnamed means including a normally open switch in series circuit with saidprimary winding and said capacitor, said transformer having a saturationcharacteristic such that substantiallythe same amount of current issupplied to wires of the same diameter but of different resistivity whenthe capacitor is charged to said predetermined voltage, suchcharacteristic existing for welding currents into and below saturationof said core, said core being driven into saturation for low impedancewires and being unsaturated when welding large impedance wires.

3. The combination according to claim 2 wherein the step-down ratio ofsaid transformer is in the range between 50 to 1 and 2000 to 1.

4. The system of claim 2 further including means for at will varyingsaid predetermined voltage between 50 and 3,000 volts. v

5. An apparatus for welding metal bodies of different resistivities andof substantially the same cross-sectional area comprising aconstant-current transformer having a primary winding and a secondarywinding, means for connecting a welding load across said secondarywinding,

mean-s including a capacitor connected across said primary winding fordeveloping a surge of current through said primary winding, saidtransformer having a core with a saturation characteristic such thatsubstantially the same amount of current is supplied to bodies of thesame cross-sectional area, but of differing resistivities, when theinitial voltage of said surge across said primary winding is apredetermined value, the saturation characteristic existing for weldingcurrents into saturation of said core, said core being driven intosaturation when welding bodies of low resistivity.

6. The combination according to claim 5 wherein said transformer furthercomprises a laminated iron core, and wherein said primary and secondarywindings are spaced from one another about said core.

'7. The combination according to claim 5 wherein said core comprises ahollow cylinder, both of said windings extending longitudinally ondifferent segments of said core.

8. A method for welding wires having differing diameters andresistivities comprising the steps of charging a capacitor to apredetermined voltage, said voltage being the same for wires of the samediameter and being irrespective of the wire resistivity, said voltagebeing higher for larger diameter wires, discharging said capacitorthrough the primary winding of a transformer with a saturable core and asecondary winding, and coupling energy from said secondary winding tothe wires being welded, said trans-former core being saturated orunsaturated during capacitor discharge when low or high resistance wiresare respectively coupled to said secondary winding for welding.

9. A method for welding wires having the same diameter and dilferingresistivities comprising the steps of charging a capacitor to a fixed,predetermined voltage, discharging said capacitor through the primarywinding of -a transformer having a saturable core and a secondaryWinding, and coupling energy from said secondary wind ing to the wiresbeing welded, said transformer core being saturated or unsaturatedduring capacitor discharge when low or high resistance wires arerespectively coupled to said secondary winding as the welding load.

'10. A method for welding bodies having differing crosssectional areasand resistivity comprising the steps of charging a capacitor to apredetermined voltage, said Voltage being fixed for wires of the samecross-sectional area of the body being welded and being irrespective ofthe body resistivity, said voltage being higher for largercross-sectional bodies, discharging said capacitor through the primarywinding of a transformer having a saturable core and a secondaryWinding, and coupling energy from said secondary winding to the bodybeing welded, said transformer core being saturated or unsaturatedduring capacitor discharge when low or high resistivity bodies arerespectively coupled to said secondary winding.

11. A method for welding bodies having fixed, predeterminedcross-sectional area but of differing resistivities comprising the stepsof charging a capacitor to a predetermined, fixed voltage, dischargingsaid capacitor through the primary winding of a transformer having asaturable core and a secondary winding, and coupling energy from saidsecondary winding to the body being welded, said transformer core beingsaturated or unsaturated during capacitor discharge when low or highresistivity bodies are respectively coupled to Said secondary winding.

12. A method capable of welding either copper or Nichrome wires of thesame diameter comprising the steps of charging -a capacitor to the same,predetermined voltage for both types of wires, discharging the capacitorthrough the primary winding of a transformer having a saturable core anda secondary winding, coupling energy induced in the secondary winding tothe wires being welded, said core being saturated or unsaturated duringcapacitor discharge when copper or Nichrome wires are respectively beingwelded.

13. A method for welding either copper or Nichrome wires of the same ordiffering diameters comprising the steps of charging a capacitor to thesame predetermined voltage for both types of wires having the samediameter, said volt-age being higher for large diameter wires,discharging the capacitor through the primary winding of a transformerhaving a saturable core and a secondary winding, coupling energy inducedin the secondary winding to the wires being welded, said core beingsaturated or unsaturated during capacitor discharge when copper orNichrome wires are respectively being welded.

14. A system for welding bodies having substantially the samecross-sectional area but different resistivities comprising a capacitor,a transformer having a saturable core, a primary winding and a secondarywinding, means for coupling the bodies to be welded across the secondarywinding, means for charging said capacitor to a predetermined voltage,means for discharging the capacitor through the primary winding of saidtransformer, said last named means including a normally open switch inseries circuit with said primary winding and said capacitor, saidtransformer having a saturation characteristic such that substantiallythe same amount of current is supplied to bodies of substantially thesame cross-sectional area but of different resistivity when thecapacitor is charged to said predetermined voltage, such characteristicexisting for welding currents into saturation of said core, said corebeing driven into saturation when bodies of low resistivity are welded.

References Cited by the Examiner UNITED STATES PATENTS 1,108,050 8/14Williams 219-108 X 1,252,144 1/18 Murray 21.9108 1,836,615 12/31 Owen336-155 2,184,628 12/39 Watson et al. 219113 2,651,701 9/53 Backen 2192,708,219 5/55 Carver 336 X 2,760,041 8/56 Yonkers 219-90 RICHARD M.WOOD, Primary Examiner.

MAX L. LEVY, Examiner.

1. A CAPACITIVE DISCHARGE SYSTEM FOR WELDING WIRES OF DIFFERENTRESISTIVITIES COMPRISING A CAPACITOR, MEANS FOR CHARGING SAID CAPACITORTO A PREDETERMINED VOLTAGE, A WELDING TRANSFORMER COMPRISING A SATURABLECORE, A PRIMARY WINDING AND A SECOND WINDING, MEANS FOR AT WILLDISCHARGING SAID CAPACITOR ACROSS SAID PRIMARY WINDING AND MEANSCONNECTING A PAIR OF WELDING ELECTRODES ACROSS SAID SECOND WINDING, SAIDTRANSFORMER HAVING A SATURATION CHARACTERISTIC SUCH THAT SUBSTANTIALLYTHE SAME AMOUNT OF CURRENT IS SUPPLIED TO WIRES OF SUBSTANTIALLY THESAME DIAMETER, BUT OF DIFFERENT RESISTIVITY, WHEN